BRAIN MACROPOTENTIALS ASSOCIATED WITH DISTINCT PHASES OF VOLUNTARY SUSTAINED ISOMETRIC CONTRACTION IN MAN

Brain potentials recorded from the scalp during voluntary sustained is ometric contraction have been consistently found to accompany both the beginning and the termination of the contraction. This study attempts to evaluate the dependence of the potentials related to the voluntary termination of a sustained effort on the physical parameters of the m otor task and also to further investigate the relationship between pot entials related to the initiation and to the termination of action. Br ain potentials from healthy male volunteers performing hand-grip squee ze were time-locked to (1) beginning of contraction; (2) execution of an additional effort; and (3) the moment of voluntary relaxation, and then averaged. The waveshape and amplitude of the entire potential cur ve preceding and following the decision to act were evaluated with bes t-fit mathematical approximation procedures. Few correlations between the various descriptive parameters of the three types of potentials we re found. The brain potentials accompanying beginning of the contracti on from state of rest differed significantly from those accompanying e xecution of an additional effort and both potentials preceding initiat ion of voluntary effort differed from potentials preceding decision to terminate the action. It is hypothesised that brain macropotentials a re linked to separate underlying commands for initiation and terminati on of voluntary action.